Acquire spinlock when updating 2PC slot data during logical decoding creation

michaelpq · michaelpq · commit 5ad165d2c024 · 2023-01-12T13:40:33.000+09:00
The creation of a logical decoding context in CreateDecodingContext() updates some data of its slot for two-phase transactions if enabled by the caller, but the code forgot to acquire a spinlock when updating these fields like any other code paths. This could lead to the read of inconsistent data. Oversight in a8fd13c. Author: Sawada Masahiko Discussion: https://postgr.es/m/CAD21AoAD8_fp47191LKuecjDd3DYhoQ4TaucFco1_TEr_jQ-Zw@mail.gmail.com Backpatch-through: 15
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
@@ -555,8 +555,10 @@ CreateDecodingContext(XLogRecPtr start_lsn,
 	/* Mark slot to allow two_phase decoding if not already marked */
 	if (ctx->twophase && !slot->data.two_phase)
 	{
+		SpinLockAcquire(&slot->mutex);
 		slot->data.two_phase = true;
 		slot->data.two_phase_at = start_lsn;
+		SpinLockRelease(&slot->mutex);
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 		SnapBuildSetTwoPhaseAt(ctx->snapshot_builder, start_lsn);
